With regard to heat pump devices in the related art such as multi-air-conditioning apparatuses for buildings, a refrigerant is made to circulate between an outdoor unit serving as a heat source unit disposed outside an architectural structure and indoor units disposed inside the architectural structure, for example. The refrigerant transfers heat or receives heat so that an air-conditioned space is cooled or heated by cooled air or heated air. An example of a refrigerant commonly used in such a heat pump device is an HFC (hydrofluorocarbon) based refrigerant. The use of a natural refrigerant, such as carbon dioxide (CO2), has also been proposed.
In a heat pump device called a chiller, cooling energy or heating energy is generated in the heat source unit disposed outside the architectural structure. A heat medium, such as water or antifreeze, is heated or cooled by a heat exchanger disposed within the outdoor unit and is transported to a fan coil unit, a panel heater, a radiator, or the like serving as an indoor unit, thereby performing a cooling operation or a heating operation (for example, see Patent Literature 1).
Another known device called exhaust heat recovery chiller uses four water pipes to connect between the heat source unit and each indoor unit and simultaneously supplies cooled water, heated water, or the like so that a cooling operation or a heating operation can be freely selected in the indoor unit (for example, see Patent Literature 2).
In another known device, a heat exchanger for a first refrigerant and a second refrigerant is disposed near the indoor units, and the second refrigerant is transported to the indoor units (for example, see Patent Literature 3).
In another known device, the outdoor unit and branch units having heat exchangers are connected by two pipes, and the second refrigerant is transported to each indoor unit (for example, see Patent Literature 4).
Furthermore, with regard to heat pump devices such as multi-air-conditioning apparatuses for buildings, there is a heat pump device that makes the refrigerant circulate from the outdoor unit to a relay unit, and makes the heat medium, such as water, circulate from the relay unit to the indoor units so as to reduce the power for transporting the heat medium while making the heat medium, such as water, circulate to the indoor units (for example, see Patent Literature 5).